1. Field of the Invention
The invention relates to a film laminate, suitable, for example, as an intermediate layer in laminated safety glazings, the film laminate being formed from at least three layers based on plasticizer-containing polyvinyl (n)acetals and/or polyvinyl (iso)acetals and having good damping properties for sound.
2. Background Art
The invention relates to a film laminate, suitable, for example, as an intermediate layer in laminated safety glazings, the film laminate being formed from at least three layers based on plasticizer-containing polyvinyl (n)acetals and/or polyvinyl (iso)acetals and having good sound damping properties.
Laminate safety glazings generally consist of two glass panes and an intermediate film connecting the glass panes. Plasticizer-containing polyvinyl butyral (PVB) is predominantly used as film material and is obtainable by reacting polyvinyl alcohol with n-butyraldehyde.
An increasingly important feature of safety glazings is the sound damping properties thereof, which can be adjusted by corresponding intermediate-layer films. To this end, intermediate films having two to five sub-layers are often used, wherein the sub-layers differ in terms of their mechanical strengths and soundproofing is thus achieved by mechanical decoupling.
Different mechanical strengths of films based on plasticizer-containing polyvinyl acetal can be set, for example, by the plasticizer content of said films or the proportion of polyvinyl alcohol groups or polyvinyl acetate groups in the polyvinyl acetal used. Generally, the mechanical strength of PVB films can be adjusted by the plasticizer content thereof or by the proportion of polyvinyl alcohol groups or polyvinyl acetate groups in the polyvinyl acetal used. For example, U.S. Pat. No. 5,340,654 or WO 2006/102049 describe multi-layer systems in which a first layer contains a polyvinyl butyral having a high residual acetate content and a second layer contains a polyvinyl butyral having a low residual acetate content. Similarly, WO 2008/137367 describes multi-layer systems in which the sub-layers made of polyvinyl butyral differ in terms of their polyvinyl alcohol content.
Due to the different residual acetate contents and different proportions of polyvinyl alcohol groups, the sub-layers have a different plasticizer content and therefore different mechanical strengths. Mechanical decoupling and therefore improved soundproofing are thus achieved.
The known multi-layer films are based on polyvinyl butyral, which is obtainable by reacting polyvinyl alcohol with n-butyraldehyde. Different plasticizer contents of the layers are obtained with use of polyvinyl(n)butyrals having different polyvinyl alcohol or polyvinyl acetate contents. This results in different mechanical properties of the layers, the greater these differences become, the greater is the soundproofing of the laminate. Good soundproofing generally results in poor mechanical properties. In addition, the layers are incompatible, that is to say there is hardly any mechanical bonding therebetween, and can slide against one another. Incompatible layers can no longer be mixed with one another, and therefore these film laminates can only be recycled poorly into the process.